Spectroscopy is analysis of a dispersed spectrum of light. A method for performing spectroscopy uses a grating spectrograph. The grating spectrograph employs a diffraction grating, a lens, and a detector array. In operation, a beam of light is dispersed by the diffraction grating. Typically, a first order diffraction is imaged by the lens onto the detector array. This produces a dispersed spectrum of light on the detector array. The detector array provides a signal to electronics which process the signal to provide an analysis of the dispersed spectrum of light.
In WDM (wavelength division multiplexed) optical communications, multiple wavelengths of light each carry a communication signal. Each of the multiple wavelengths of light forms a channel. In DWDM (dense WDM) optical communication, a subset of the WDM optical communication, the channels are spaced close together. A typical DWDM application operates at a wavelength band about 1,550 nm, has 80 channels, and has spacing of 0.4 nm between adjacent channels.
In WDM optical communications there is a need to monitor the wavelength and power level of each channel. This is especially required for DWDM optical communications because of the close spacing between adjacent channels.
A method of monitoring the WDM channels employs a grating spectrograph where the dispersed spectrum is a WDM wavelength band.
The grating spectrograph has a number of deficiencies which reduce a quality of the analysis of the dispersed spectrum of light. Because the grating spectrograph images the dispersed spectrum of light onto the detector array, the grating spectrograph's stability and sensitivity is limited by the detector array's number of detecting elements. Because the sensitivity of the detector array is limited, resolution of the detector array is also limited. Further, because the grating spectrograph images the dispersed spectrum of light onto the detector array, the grating spectrograph is susceptible to 1/f noise and drift. Moreover, because the grating spectrograph images the dispersed spectrum of light onto the detector array, the detecting elements are susceptible to saturation. In other words, the detecting elements have limited dynamic range.
What is needed is a method of analyzing a dispersed spectrum of light which is stable, sensitive, economical, and which provides greater resolution.
What is needed is a method of analyzing a dispersed spectrum of light which provides greater dynamic range, which is not subject to 1/f noise, and which is not subject to drift.
What is needed is a method of monitoring WDM channels which is stable, sensitive, cost efficient, and which provides greater resolution.
What is needed is a method of monitoring WDM channels which provides greater dynamic range, which is not subject to 1/f noise, and which is not subject to drift.